Voltage comparator circuits are used in a number of applications to compare an input voltage with a reference voltage and indicate whether the input voltage is greater or less than the reference voltage. In one example, voltage comparator circuits have been used with memory read or retrieval devices to detect the data stored in a data storage device, such as a flash memory device. A flash memory device may have a large number of storage elements for storing data (e.g., one bit or two bits per storage element). During the process of reading the flash memory device, a read device may apply a pre-determined voltage across the terminals of a storage element to determine the status of the storage element, such as the presence of data in the storage element or an indication of an erased storage element or programmed storage element.
If the storage element has been erased, the storage element may draw a substantial amount of current (e.g., 40 μA) in response to the voltage application. If the storage element has been programmed, the storage element may draw significantly less current (e.g., 3 μA) in response to this voltage application. Using a voltage comparator having a reference current (e.g., 20 μA) between these two currents and current-to-voltage converters, the voltage comparator may determine whether the current drawn by the storage element is greater than or less than the reference current and thus determine the status of each storage element (e.g., erased or programmed) in the flash memory device.
In some conventional voltage comparators, the rate of comparing an input voltage with a reference potential may be compromised by the number of dominant poles, within the voltage comparator, having an associated load impedance (e.g., input impedance from transistors at a particular circuit node in the voltage comparator). For example, some conventional voltage comparators with a greater number of dominant poles may have a slower comparison rate. Memory read or retrieval devices incorporating these voltage comparators generally have slower read rates. While limiting the number of these dominant poles may tend to increase the comparison rate, the range of input voltage may be sacrificed (e.g., a smaller input voltage range) and decrease the sensitivity of the voltage comparator.
Accordingly, a voltage comparator circuit is desired having a relatively fast voltage comparison. In addition, a voltage comparator circuit is desired for rail-to-rail input voltage comparison. In addition, a method for voltage comparison is desired having a relatively fast comparison of an input voltage while increasing sensitivity. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.